1. Field of the Invention
This invention relates to curable epoxy resins. More particularly it relates to one and two component epoxy resin compositions which are useful as flexible adhesives and which do not rely upon a solvent for their low viscosity.
2. Prior Art
Epoxy resins constitute a broad class of polymeric materials having a wide range of physical properties. The resins are characterized by epoxide groups which are cured by reaction with certain catalysts or curing agents to provide cured epoxy resin compositions with certain desirable properties.
The most common epoxy resins are a condensation product of epichlorohydrin and bisphenol A. This system can be cured with any of the conventional curing agents such as polyamines, polycarboxylic acids, anhydrides and Lewis acids. Bisphenol A based epoxy compositions when cured have good adhesive properties but many are inherently stiff and brittle and hence their use is limited to applications where tensile shear forces do not come into play.
It has been found that plasticizers can be added to the epoxy resin adhesive system to improve flexural strength. Typical methods of plasticization include the addition of flexibilizing aliphatic amines to the curing agent, addition of aminated or carboxylated rubbers to the system, addition of carboxy-terminated polyesters, addition of organic hydroxyl containing compounds and the addition of epoxidized oils.
In H. N. Vazirani Adhesives Age 23, No. 10, p. 31 is described reaction products of liquid epoxy resins with a polyoxypropylene diamine which are useful in flexibilizing adhesive systems.
It is well known in the art that there is a need for an epoxy system that will produce a flexible cured resin with good adhesive properties.